Cognitive Function in Non-Insulin Dependent Diabetic Patients : P300 Event-related Potentials and Neuropsychological Tests

ABSTRACT

BACKGROUND AND OBJECTIVE: Several recent studies have demonstrated that cognitive function is impaired in non-insulin dependent diabetes mellitus (NIDDM) patients compared with age-matched non-diabetic controls. However, the underlying pathophysiological mechanism of this diabetic central nervous involvement remains obscure. The present study was designed to explore further whether cognitive deficits are present in NIIDDM patients who do not show apparent symptoms and signs of central nervous system damage and to evaluate the influence of clinical parameters and diabetic complications on cognitive function. METHODS: Thirty patients over 50 years of age with NIDDM and 30 age-, sex- and education-matched normal controls were recruited for the study. P300 event-related potential test and neuropsychological tests (Mini-Mental State Examination, MMSE; Benton Visual Retention test; Digit Span Forward and Backward) were perfomed. P300 latencies were recorded according to the conventional technique using Counterpointer MK2. RESULTS: Compared with controls, NIDDM patients showed significant impairment in MMSE (P<0.05), Benton Visual Retention (P<0.05), and Digit Span Backward (PNIDDM patients (P<0.05), and 4 patients showed values above the reference value range. P300 latencies and neuropsychological test scores were not clearly correlated with duration of NIDDM, duration of neuropathy, fasting blood glucose, HbA1c serum triglyceride and 24 hour urine protein. Compared with controls, P300 latencies were prolonged in diabetic patients with peripheral neuropathy, nephropathy, and retinopathy, but neuropsychological tests, such as MMSE, Benton Visual Retention and Digit Span Backward, scores were decreased in diabetic patients without retinopathy and nephropathy. P300 latencies were not in correlation with neuropsychological test scores both in NIDDM patients and in nomal controls.

CONCLUSIONS:

This study suggest that 1) cognitive function is decreased in NIDDM patients who do not show apparent symptoms and signs of central nervous system damage, 2) P300 latency may reveal cognitive changes not detected by nouropsychological tests, and 3) P300 event-related potentials, MMSE, Benton Visual Retention and Digit Span Backward tests may be included in a battery of cognitive function tests in NIDDM patients.